1. Field of the Invention
The present invention relates to a memory module and in particular to a memory module with a heat dissipation means for the reduction of the temperature of memory devices of the memory module.
2. Description of the Related Art
A substantial parameter with DRAM (Dynamic Random Access Memory) memory devices is the retention time during which each memory cell of the memory device maintains information stored therein in form of an electrical charge in a securely readable manner. The longer the retention time, the lower the electric power required for refreshing the memory cells on a temporal average. Particularly for battery-operated applications, such as for mobile radio applications, a power need as low as possible is desired. Usually a retention time of about 64 ms is required. The retention time is determined by the electrostatic capacity of a capacitor which every single memory cell has and various parasitic leakage currents via which the capacitor looses its charge. The progressive miniaturization and the growing integration density of DRAM memory devices require increasingly smaller circuit geometries. Due to the increasingly smaller circuit geometries, it becomes more and more difficult to manufacture DRAM memory devices. In particular, ever-increasing expenditure is required to implement the capacity of about 20 fF to 40 fF of the capacitor of each single memory cell. Hereby, especially the yield of those memory devices whose entire memory cells meet the requirement for the retention time decreases in the manufacturing process.
The leakage currents causing the gradual loss of the memory cell charge are temperature-dependent. The higher the semiconductor temperature or the temperature of the semiconductor material of the memory device, the higher the leakage currents. A temperature difference of about 2° C. to 3° C. already causes a change in the retention time of 10 ms to 15 ms.
Most of the memory devices manufactured today are sold in form of memory modules or memory groups. A memory module has a board onto which usually a plurality of memory devices is soldered.
FIG. 3 shows an example for a conventional memory module with a board 10 onto the front on which four single memory devices 12 are mounted. The memory module is connected in an electrically conductive manner via a contact bar 14 or a linear arrangement of contact pins or contact pads to an application, such as a motherboard of a computer system. The memory module is usually plugged in a corresponding socket which is arranged on a motherboard of a computer, for example. During the operation, heat or waste heat develops in the memory devices 12. It is given off or dissipated either by direct emission or convection to the environment or by the electrical contacts 16 to the memory module board 10. The dissipation of the waste heat via the electrical contacts is the mostly dominating heat dissipation mechanism today. This is especially the case for the memory devices 12 in TSOP (thin small outline device) housings.